1. Field of the Invention
The present disclosure relates to a method of manufacturing an image pickup device that has a plurality of light guiding members.
2. Description of the Related Art
It has been proposed that light guiding paths (optical waveguides) that guide light to photoelectric conversion portions are provided in image pickup devices such as complementary metal oxide semiconductor (CMOS) sensors. In an example of known methods, such light guiding paths are formed as follows. That is, a plurality of openings are initially formed in a base film formed of a silicon oxide layer, and then a silicon nitride filling member is formed as a film so as to fill in the plurality of openings. Excessive part of the filling member spread out of the openings is removed by using a chemical mechanical polishing (CMP) method. Thus, silicon nitride light guiding members have been formed.
Japanese Patent Laid-Open No. 2009-164247 discloses an image pickup device that has an effective pixel region, in which photoelectric conversion portions are arranged, and a peripheral region, which surrounds the effective pixel region. In the image pickup device, the level of an upper surface of a filling member is different between the effective pixel region and the peripheral region. Since the level is higher in the peripheral region than in the effective pixel region, in a technology disclosed in Japanese Patent Laid-Open No. 2009-164247, a dummy opening is provided in the peripheral region so as to reduce the difference in level that exists in a boundary portion between the effective pixel region and the peripheral region.
Since circuit wiring is provided in the peripheral region, it may be difficult in some cases to desirably form the dummy opening described in Japanese Patent Laid-Open No. 2009-164247. This limits the reduction of the difference in level of the upper surface of the filling member. Furthermore, such a difference in level causes a problem in particular when the filling member is removed until a base film is exposed, so that a plurality of light guiding members are formed. That is, when not only the excessive part of the filling member spread out of the openings on the image pickup region but also the filling member in the openings and the base film are removed, the length of the light guiding members becomes non-uniform in the image pickup region. Non-uniformity in the length of the light guiding members causes degradation of imaging performance such as variation in the optical interference conditions among the light guiding members.